1. Field of the Invention
The present invention concerns a torsional damper comprising at least two coaxial parts mounted to rotate relative to one another within a defined range of relative angular movement and circumferentially acting elastic means between said parts resisting such relative angular movement.
2. Description of the Prior Art
This type of torsional damper is normally incorporated in the design of a friction clutch plate, particularly for automotive vehicles, in which case one rotating part comprises a friction disk designed to rotate with a first shaft, in practice a driving shaft and the motor output shaft in the case of an automotive vehicle, whereas the other of said rotating parts is carried on a hub designed to rotate with a second shaft, in practice a driven shaft and the gearbox input shaft in the case of an automotive vehicle.
This type of device is used to permit regulated transmission of rotational torque applied to one of its rotating parts where the other is itself subject to a rotational torque. It is thereby able to filter vibrations which may arise at any point in the kinematic system in which it is incorporated, extending from the motor to the driven road wheels in the case of an automotive vehicle.
In practice, this type of torsional damper further comprises friction means operative between its constituent rotating parts and generating a friction torque between them, in one direction or the other. This produces a "hysteresis" effect, that is to say a difference, for the same value of relative angular movement between the rotating parts, between the value of the torque transmitted from one rotating part to the other for one sense of change in the torque and the value of this torque for the opposite sense of change thereof, favouring the filter action required.
These friction means usually comprise one or more friction rings acting axially between the rotating parts concerned.
It has been proposed, however, in particular in U.S. Pat. No. 2,826,902, to substitute for such friction rings at least one friction pad which is constrained to rotate with one of the rotating parts concerned and is in rubbing engagement with an axial surface constrained to rotate with the other rotating part, thus acting radially between the rotating parts.
One advantage of this type of friction pad is that it is responsive to centrifugal force, so that its effect increases as the rotational speed of the damper assembly increases. In some applications at least, this is favourable to the filtering of vibration producing noise.
Another advantage is that it is a simple matter to combine such a friction pad with elastic means of relatively low stiffness acting between the rotating parts concerned over a relatively extended range of relative angular movement therebetween, also favouring the required filter action.
In the aforementioned U.S. Pat. No. 2,826,902, the friction pads are in rubbing engagement with an axial surface which is circular in transverse cross-section.
While this arrangement can give satisfactory results, at least in certain applications, it has the disadvantage that the hysteresis effect due to the friction pads is independent of the degree of relative angular movement between the rotating parts concerned.
The general object of the present invention is to provide an arrangement which, using friction pads of this type, provides a hysteresis effect which varies with the degree of relative angular movement between the rotating parts concerned, permitting an extension to the field of application of such friction pads.